feat: Allow passing a custom registry to be used instead of using the default one

[tiangolo]

✨ Allow passing a custom registry to be used instead of using the default one.

This would be useful in particular when testing multiple FastAPI apps (e.g. microservices) in the same tests run.

This is also related to #80

Note: I'm still having issues with this in different corner cases. The way that the underlying Prometheus Client for Python works is quite weird. It errors out if a metric is duplicated, but there's no way to check if a new metric will create that error or not. And a try block would have to be very generic catching all ValueErrors. I'm still not sure what's the best way to handle this.

[ChuckHend]

I'd love to see this go out!

[trallnag]

Thank you, @tiangolo. Sorry for ignoring your work for a long time

[trallnag]

Hmm I just did a poetry update and suddenly test_expose_defaults() started to fail.

info = <prometheus_fastapi_instrumentator.metrics.Info object at 0x7f232b7433d0>

    def instrumentation(info: Info) -> None:
>       TOTAL.labels(info.method, info.modified_status, info.modified_handler).inc()
E       NameError: free variable 'TOTAL' referenced before assignment in enclosing scope

src/prometheus_fastapi_instrumentator/metrics.py:628: NameError

Before that it worked fine. It tried to debug it. The Prometheus client lib is complaining about duplicate metrics as excepted.

Duplicated timeseries in CollectorRegistry: {'http_requests_total', 'http_requests_created', 'http_requests'}

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Problems start when updating starlette and fastapi

  • Updating starlette (0.22.0 -> 0.25.0)
  • Updating fastapi (0.88.0 -> 0.92.0)